CS 141 Computer Programming 1

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CS 141Computer

Programming 1

Teacher AssistantHadeel Al-Ateeq

Branching Statements

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Outline Control Structure. Control Structures in C++. Sequence Structure. Selection Statements. If- single selection statement. If else – double selection statement. Conditional Operators. Nested if-else statements. Dangling else Problem. Using Boolean Variables. Implicit Typecasting. Switch – multiple selection statement. Questions.

Control Structure (Logic Structure)

Sequence structure: Process one instruction after another in the order they

are written. Selection structures:

Decision structure Make choices by using relational or logical

operators. Case structure

Enable to pick up one of a set of tasks. Repetition structure:

Enable to repeat tasks.

Control Structures

C++ Control

Structure

Sequence structure

Selection Structure

If, if… else, switch

Repetition structure

While, do…while, for

Control structures in C++

Models the workflow (activity) of a portion of a software system

Add grade to

total

Add 1 to counter

Corresponding C++ statement:total=total + grade;

Corresponding C++ statement:counter=counter + 1;

Sequence StructureActivity Diagram

Action states contains action

expressions

Transitions order in which actions occur

Initial State Beginning of the

workflow

Final State End

of the workflow

Notes Describe the purpose of

the symbols

Dotted line connects each

note with element it describes

Selection Statements

Types

Single selection statement

Double-selection statement

Multiple-selection

statementSelects or ignores a single

group of actions.Selects among many

group of actions.

Selects between two groups of actions.

Use the keyword if. Begin with if followed by condition; then action

or group of actions (compound statements or blocks) are listed.

Enclose compound statements between braces {} and indent these statements.

If condition is true , action is performed. Otherwise, actions is ignored.

if (grade >=60) cout<<“Passed”;

Example: Pseudocode:If student grade is

greater than or equal to 60

Print “Passed”

If - Single Selection Statement

Grade >=60

Grade<60

Print “Passed”

Activity Diagram


Decision Symbol indicates that a decision

to be made

if (condition)action;

if (condition){

action1;action2;…..….….actionN;

}

Condition can be relational or equality operators or any other

expressionsZero False

nonzero True


Single Action

Multiple Actions surrounded by

braces {}

Use the keyword if and else. Begin with if followed by condition; then

action or group of actions are listed. End with else then action or group of

actions are listed. If condition is true, action that followed by if

is performed. Otherwise, action that followed by else is

performed.

if…else-Double-selection Statement

if (condition)action1;

elseaction2;

if (condition){

action1;…..actionN;

}else{

action1;….actionN;

}

Single Action

Multiple Actions surrounded by

braces {}

Condition can be relational or equality operators or any other

expressionsZero False

nonzero True


Grade >=60Grade<60 Print “Passed

”

Print “Failed”

Activity Diagram


If (grade >=60) cout<<“Passed”; else

cout<<“Failed”;

Pseudocode:if student's grade is

greater than or equal to 60

Print “passed”Else

Print ”failed”

Example


Provide similar result of if…else double selection statement.

Ternary operator requires three operands: Condition. Value when condition is true. Value when condition is false.

Syntax: (Condition? Condition’s true value:

condition’s false value)

Conditional Operator (?:)

Grade >=60 ? cout<<“Passed”: cout<<“Failed”;

Conditional Operator (?:)Example

cout<<(grade >=60 ? “passed”: “failed”);

Can be written as:

int i=1, j=2, max;max=(i>j ?i:j);

Example Precedence of the conditional operator is low

One inside another, test for multiple cases Once condition met, other statements

skipped.

Nested if.. else Statements

Example

if (conditioin1)action1;

elseif (condition2)

action2;else

if(condition3)action3;…

else

actionN;


if (condition1){

if (condition2)action1;

else{

if (condtion3)action2;

elseaction3;

}}else

action4;


Write a C++ program that prints A for exam grades greater than or equal to 90, B for grades in the

range 80 to 89, C for grades in the range 70 to 79, D for grades in the range 60 to 69 and F for all other

grades.


Question



Nested if.. else StatementsAnother

Solution

Nested if.. else StatementsAnother Solutio

n

x=10; y=2;if (x>5)

if(y>5)cout<<“x and y are >5

“<<endl;else

cout<<“x is <=5”<<endl;

Each else associated with immediately preceding if

There is an exception when placing braces {}

Logical error !!

Dangling –else Problem

Example

x=10; y=2;

if(x>5){

if(y>5)cout<<“x and y are >5”<endl;

}

elsecout<<“x is <=5”;

Dangling –else ProblemCorrectnes

s

Block

Example

Dangling –else Problem

bool flag1, flag2;

if (flag1)----else----

if( flag1|| flag2)----

else-----

Using Boolean variables

int x1,x2;

if(x1)…

else…

if(x1||x2)…

else….

Implicit Typecasting

Confusing the equality operator == with the assignment operator = results in logic errors.

int x=0;if (x=2)

cout<<"x is equal to 2";else

cout<<"x is not equal to 2";

This message will always be printed

!!

Note

Example

int X=0;X==1;

X’s value will remain

0

Perform actions based on possible values of variable or expression.

Use keywords switch, case, default and break. Begin with switch followed by controlling expression

enclosed between parentheses (). Value of the controlling expression is compared with

each case label, then if a match occurs the program executes action for that case.

No matching, the program executes the optional default statement.

Switch - Multiple-selection Statement

Break Keyword

Causes immediate exit from switch statement. Jumps out of the switch statement, and do not execute

any more code.

[True]

case a action(s)

Activity Diagram

Switch - Multiple-selection Statement

break

case b action(s)

break

case z action(s)

break

default action(s)

[True]

[True]

[False]

[False]

[False]

[False]

case a

case b

case z

switch (expression){

case value1:action1;break;

case value2:action2;break;

….case valuen:

actionN;break;

default:action;

}

Switch Multiple-selection Statement

switch (number){

case 0: cout<<“too small, sorry!”;break;case 5: cout<<“good job!”<<endl; //fall through

case 4: cout<<“nice pick!”<<endl; //fall through

case 3: cout<<“excellent !”<<endl; //fall through

case 2: cout<<“masterfull!”<<endl; //fall through

case 1: cout<<“incredible!”<<endl; //fall through

break;}

Switch Multiple-selection StatementExample

Question #1

Write a C++ program that outputs the fine for driving too fast. It takes BOTH the

speed limit and current speed, compares between them and prints the

appropriate fine as follows:

You are lucky!, if the result of comparison is less than 10.

Fine payable: 40 Dollars, if the result of comparison is in the range of 10 and 20.

Fine payable: 80 Dollars, if the result of comparison is in the range of 20 and 30.

Hand over your driver’s license!, otherwise

Question #1

Question #1

Question #2

Write a C++ program that calculates the minimum of two input numbers.Note: check the validity of the

inputs

Question #2

Question #2

Question #3

Write a C++ program that calculates the maximum of two input numbers.Note: check the validity of the

inputs

Question #3

Question #3

State the output for each of the following:

When x is 9 and y is 11. When x is 11 and y is 9.

Question #4

Output

if(x<10)if(y>10)cout<<“*****”<<endl;elsecout<“#####”<<endl;cout<<“$$$$$”<<endl;

*****$$$$$

$$$$$

if(x<10){if(y>10)cout<<“*****”<<endl;}else{cout<<“#####”<<endl;cout<<“$$$$$”<<endl;}

Question #4

State the output for each of the following:

When x is 9 and y is 11. When x is 11 and y is 9.

Output

*****

#####$$$$$

Write a C++ program that compares any two integers using if

statements, relational operators and equality operators.

Question #5

Sample Output:

Question #5

Question #6

Write a C++ program that prints out the entered character choice.

It accepts only three characters a, b and c (upper or lower cases).

Otherwise it prints“Your choice is not defined”

Note: Use Switch Statement

Question #6

Question #6

Question #7

Trace the following code segment and show the value of value

variable.

Value

Cannot be determined

because the value of input variable

is unknown

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CS 141 Computer Programming 1